Frequently in the television industry it is desirable to convert motion pictures or other image media such as video tape into video signals for recording or for transmission of the images to a viewing audience. Many technical problems are encountered in converting the motion picture images into video signals, including problems in the spectral response of the color dyes in the film, the characteristics of the telecine, and the fact that the characteristics of the photographic film are not matched to the electronic components used in the telecine or "film chain". Especially, problems are encountered in insuring that the spectral content of the resultant video signals are aesthetically acceptable and that the luminance or monochrome portion of the video signal provides an acceptable black and white image when reproduced on monochrome equipment.
One proposal for a color correction system for use in a film chain is shown in U.S. Pat. No. 4,096,523 to Belmares-Sarabia et al. In this system, color corrections are made in the video signals by adjusting the color hue and saturation, and by varying the proportions of the primary color video signals to form a composite luminance signal. The entire film is color-corrected by providing incremental adjustment signals which are added to or subtracted from standard values for each different scene in the film. The incremental adjustment values are stored in a computer memory associated with an event number, which is in turn associated with the count of the frame in the film at which the color correction was made.
After a series of color corrections have been made, a video tape recording of the color-corrected video signals is produced by re-running the motion picture film, video tape, or other video media through the system, while the color correction incremental adjustment signals are recalled from memory and added to the signals produced during the running of the film. The resultant color-corrected composite video signals are then recorded on the video tape recorder.
The Belmares-Sarabia patent discloses means for automatically returning the color potentiometers for color parameters and luminance correction quickly to a starting position in preparation for another color correction. The control potentiometers are adapted to be moved from a starting position to vary the magnitude of one of the color components. Magnetic positioning devices are used to reset the potentiometers to the zero or null position at the start of the next color correction, during the vertical video interval. A DC pulse from the control circuitry provides an electromagnetic field in the magnetic positioning device in response to actuation of a "mark event" pushbutton in coincidence with the vertical sync signal. The potentiometers are then returned by the magnetic positioning device to the starting positions regardless of whether the potentiometers have been turned clockwise or counterclockwise. The values represented by the settings of the potentiometers are stored in a memory so that when the motion picture film is re-run, those values can be recalled from memory in order to effectuate the color correction.
While the system shown in this patent conveniently allows repetitive corrections to be made without forcing tedious and repetitive manual resetting of the potentiometers, the apparatus is basically electromechanical in nature and requires large amounts of energy in surges to simultaneously reset all of the potentiometers. Accordingly, the mechanical resetting of the potentiometers is noisy, energy inefficient, and imparts vibrations to the components which shortens the life of other electronic components.
The prior art does not provide a color correction system including control or adjusting means for adjusting the spectral content or other parameters, which means does not suffer from the disadvantage that components must be physically and mechanically returned to a starting position in preparation for a second and subsequent color correction.
Another difficulty encountered in the use of the color correction system shown in the Belmares-Sarabia patent occurs when it is desired to return to a previously-made scene correction and re-correct one or more parameters of that scene. In order to accomplish this task with the apparatus shown in the patent, it is necessary to recall from memory the correction values associated with the frame count for which a revised correction is desired. Ideally, the effects of these recalled correction values should be displayed on the color monitor superimposed on the scene being re-corrected, but there appears to be no provision for resetting the correction potentiometers to the stored correction values other than by manual resetting; the automatic-return magnetic positioning devices appear to be unable to set the potentiometers to a predetermined, stored setting.